Modeling extraction equilibria of butyric acid distributed between water and tri-n-butyl amine/diluent or tri-n-butyl phosphate/diluent system: Extension of the LSER approach

Abstract

Extraction of butyric acid from water by tri-n-butyl amine and tri-n-butyl phosphate dissolved in oxygenated polar diluents of proton-donating and proton-accepting types (1-octanol, acetophenone, ethyl butyrate, ethyl pentanoate, ethyl nonanoate, diethyl malonate), as well as a comparison with extraction equilibria of pure diluent alone have been studied at 298K. Among the tested diluents, 1-octanol alone yields the highest extraction efficiency. The strength of complex formation is larger for tri-n-butyl amine as compared to tri-n-butyl phosphate both favoring mainly the formation of acid1–extractant1 structure. Ethyl butyrate promotes more readily the solvation of the formed organic phase complexes.The distribution data have been subjected to formulation of multivariable correlations depending on LSER (linear solvation energy relation) and mass action law principles. LSER-based solvation model involving five physical descriptors is able to simulate satisfactorily distribution properties of butyric acid yielding 1.7% mean error and satisfies established limiting behavior of the physical event. The mass action law chemodel, comprising the formation of one or two acid–extractant complexes proved to be slightly less accurate yielding 4.5% mean error. The modified Langmuir model is quite accurate in reproducing the observed properties with 1.5% mean error.